1. Field of the Invention
The present invention relates to a control valve for variable capacity compressors used in air conditioners of vehicles and the like and, more particularly, to a control valve for variable capacity compressors that controls the supply of a coolant gas in the interior of a crankcase from a discharge-pressure region as required.
2. Description of the Prior Art
Conventionally, variable capacity compressors provided with a cylinder, a piston, a wobble plate, etc. have been used, for example, in compressing and delivering a coolant gas of an air conditioner for automobiles. A known variable capacity compressor of this type is provided with a coolant-gas passage that communicates with a discharge-pressure region and a crankcase, and changes the inclination angle of the wobble plate by adjusting the pressure in the interior of the crankcase thereby to change discharge capacity. The pressure adjustment in the interior of the crankshaft is performed by supplying a high-pressure compressed coolant gas from the discharge-pressure region to the crankcase by the opening adjustment of a control valve provided within the coolant-gas passage.
For example, a control valve 100xe2x80x2 as shown in FIGS. 10 and 11 is known (Japanese Patent Application Laid-Open Nos. 9-268973 and 9-268974) as a control valve for such a variable capacity compressor as described above. This control valve 100xe2x80x2 is provided on the side of the rear housing 210 of a variable capacity compressor 200, and performs the pressure adjustment of a crankcase 231 within a front housing 230, which is installed in connection with a cylinder block 220 of the variable capacity compressor 200.
In the interior of the crankcase 231, a wobble plate 240 is supported by a driving shaft 250 in a manner such that the wobble plate 240 can slide in the axial direction of the driving shaft 250 and tilt. A guide pin 241 of this wobble plate 240 is slidably supported by a support arm 252 of a rotary support 251. Also, the wobble plate 240 is connected, via a pair of shoes 242, to a piston 260, which is slidably disposed within a cylinder bore 221.
The wobble plate 240 rotates in the directions indicated by an arrow shown in FIG. 10 according to a difference between the suction pressure Ps in the cylinder bore 221 and the crankcase pressure Pc in the crankcase 231, and changes the inclination angle of the wobble plate 240 itself. On the basis of the inclination angle of the wobble plate 240, the stroke width of forward and backward movements of the piston 260 in the cylinder bore 221 is determined. And a blocking element 270 that abuts against the middle portion of the wobble plate 240 moves forward and backward in a housing hole 222 as the wobble plate 240 rotates in the directions indicated by the arrow.
In the interior of the rear housing 210, suction chambers 211a, 211b, which constitute a suction-pressure region, and discharge chambers 212a, 212b, which constitute a discharge-pressure region, are defined and formed. When the piston 260 moves forward and backward on the basis of the rotation of the wobble plate 240, a coolant gas in the suction chamber 211a is sucked into the interior of the cylinder bore 221 from a suction port 213, is compressed to a prescribed pressure and is then delivered from a discharge port into the discharge chamber 212a. 
Furthermore, a suction passage 215 formed in the center portion of the rear housing 210 communicates with the housing hole 222 and, at the same time, the suction passage 215 communicates also with the suction chamber 211b via a through hole 216. When the wobble plate 240 moves to the side of the blocking element 270, the blocking element 270 moves to the side of the suction passage 215 and blocks the through hole 216.
The upper side of the control valve 100xe2x80x2 communicates with the suction passage 215 via a pressure-detection passage 217 that introduces the suction pressure Ps into the interior of the control valve 100xe2x80x2. Furthermore, the discharge chamber 212b and the crankcase 231 communicate with each other via air supply passages 218, 219 of the control valve 100xe2x80x2. The air supply passages 218, 219 are opened and closed by a valve element 106xe2x80x2 of the control valve 100xe2x80x2.
The discharge pressure Pd of the discharge chamber 212b is introduced into a valve chamber port 113xe2x80x2 via the air supply passage 218. The pressure Pc within the crankcase is introduced into the air supply passage 219 via a valve hole port 114xe2x80x2. The suction pressure Ps is introduced into a suction pressure introduction port 115xe2x80x2 via the pressure-detection passage 217.
When an operation switch 280 of an air conditioner is on, for example, when a temperature detected by a room sensor 281 is not less than a temperature set by a room temperature setting device 282, a control computer 283 gives instructions to a solenoid 101xe2x80x2 of the control valve 100xe2x80x2 and causes the solenoid 101xe2x80x2 to supply a prescribed current to a driving circuit 284. And a moving core 102xe2x80x2 is attracted toward the fixed core 104xe2x80x2 by the attraction of the solenoid 101xe2x80x2 and the urging force of a spring 103xe2x80x2.
With the movement of the moving core 102xe2x80x2 the valve element 106xe2x80x2 attached to a solenoid rod 105xe2x80x2 moves, while resisting the urging force of a forced relief spring 107xe2x80x2, in a direction in which the opening of a valve hole 108xe2x80x2 is reduced. With the movement of this valve element 106xe2x80x2 a pressure-sensitive rod 109xe2x80x2, which is integral with the valve element 106xe2x80x2, also rises. As a result of this, a bellows 111xe2x80x2 is pressed, which is connected to the valve element 106xe2x80x2 via a pressure-sensitive rod receiving part 110xe2x80x2 in such a manner that the bellows 111xe2x80x2 can come close to and away from the valve element 106xe2x80x2.
The bellows 111xe2x80x2 is displaced according to variations in the suction pressure Ps introduced into the interior of a pressure-sensitive part 112xe2x80x2 via the pressure-detection passage 217, and gives loads to the pressure-sensitive rod 109xe2x80x2. Accordingly, the opening of the valve hole 108xe2x80x2 of control valve 100xe2x80x2 by the valve element 106xe2x80x2 is determined by a combination of the attraction by the solenoid 101xe2x80x2, the urging force of the bellows 111xe2x80x2 and the urging force of the forced relief spring 107xe2x80x2.
When a difference between a temperature detected by the room sensor 281 and a temperature set by the room temperature setting device is great (when the cooling load is large), an increase in supply current causes the fixed core 104xe2x80x2 to attract the moving core 102xe2x80x2, and the opening of the valve hole 108xe2x80x2 by the valve element 106xe2x80x2 decreases. As a result, the control valve 100xe2x80x2 operates in such a manner that the control valve 100xe2x80x2 holds a lower suction pressure Ps, and under this suction pressure Ps the opening and closing of the valve element 106xe2x80x2 is performed.
When the valve opening decreases, the volume of the coolant gas that flows from the discharge chamber 212b via the air supply passages 218, 219 into the crankcase 231 decreases and, at the same time, the gas in the crankcase 231 flows out and enters the suction chambers 211b, 211a, with the result that the pressure Pc in the crankcase drops. And when the cooling load is large, the suction pressure Ps in the cylinder bore 221 increases and a difference is made between the suction pressure Ps and the pressure Pc in the crankcase, resulting in an increased inclination angle of the wobble plate 240. As a result, the blocking element 270 leaves the side of the suction passage 215 and opens the through hole 216.
Incidentally, as shown in FIGS. 10 and 11, the above-described conventional control valve 100xe2x80x2 is constructed in such a manner that the discharge pressure Pd is introduced into the valve chamber port 113xe2x80x2 of the control valve 100xe2x80x2 via the air supply passage 218. This discharge pressure Pd is high and besides the coolant gas that generates the discharge pressure Pd gives off high heat by being compressed by the forward and backward motions of the piston 260 until a prescribed pressure is reached, with the result that the control valve 100xe2x80x2 itself is heated by this high heat and the accuracy of opening and closing of the valve hole 108xe2x80x2 by the valve element 106xe2x80x2 decreases, posing a problem.
Also, because the distance between the point of application of the attraction of solenoid rod 105xe2x80x2 by the solenoid 101xe2x80x2 and the point of application of the urging force by the bellows 111xe2x80x2 is large, there is a fear that during the movement of the solenoid rod 105xe2x80x2 at the time of valve closing, backlash might occur in the solenoid rod 105xe2x80x2, thereby hindering an improvement in the accuracy of valve opening and closing.
In order to solve this problem, there is disclosed in Japanese Patent Application Laid-Open No. 11-218078 a technique for bringing the point of application of the attraction of solenoid rod close to the point of application of the urging force of bellows by disposing a bellows below a solenoid rod. With this technique, however, a low suction pressure Ps becomes apt to remain as a coolant pool on the bellows side and, therefore, no special consideration is given to factors responsible for the hindrance to plunger motions, such as sticking by plane contact between the lower end of the control valve proper and the upper end surface of the plunger, or factors responsible for the hindrance to the motions of the plunger and stem by the damper action of a coolant.
Furthermore, the pressure-receiving area that receives the crankcase pressure Pc on the upper side of the moving direction of the valve element 106xe2x80x2 is adjusted to such a size that the respective pressure-receiving areas of valve hole 108xe2x80x2 and solenoid rod 105xe2x80x2 are not affected by pressure. However, because the suction pressure Ps and crankcase pressure Pc are not always held at the same level of pressure, the suction pressure Ps and crankcase pressure Pc are not completely balanced out. In addition, because the pressure in the crankcase shows great pressure variations due to the operation of a compressor, forces acting on the valve element 106xe2x80x2 also vary when the pressure variations occur, posing a problem of an adverse effect on the opening and closing accuracy of the valve element 106xe2x80x2.
Also, in the conventional control valve for variable capacity compressors, a pressure-sensitive bellows and means for exciting a solenoid are arranged side by side in the opening and closing direction of a valve element and, therefore, this poses a problem of difficulty in achieving compact design suitable for a part to be installed in a car.
An object of the present invention is to provide a control valve for variable capacity compressors which improves the accuracy of valve opening and closing by eliminating an adverse effect of a coolant gas pressure acting on the valve element of the control valve, and which, at the same time, permits compact design.
In order to achieve the above-described object, in a first aspect of the present invention there is provided a control valve for variable capacity compressors, which comprises a control valve body, a solenoid excitation part and a pressure-sensitive part. The solenoid excitation part is provided with a solenoid and a plunger moving vertically by the excitation of the solenoid. The control valve body is disposed on the upper side of the solenoid excitation part and has a valve chamber provided with a valve hole on the bottom surface thereof, a pressure chamber disposed above the valve chamber, and a valve element disposed in the valve chamber and performing opening and closing operations by the plunger. The upper end of the valve element of the control valve body is inserted in the pressure chamber and the lower end thereof is inserted in the plunger chamber of the solenoid excitation part. And, the plunger chamber and the pressure chamber communicate with each other through a cancel hole formed in the valve element.
Because in the control valve for variable capacity compressors of the present invention constructed as described above, the coolant gas at the suction pressure Ps in the plunger chamber is introduced into the pressure chamber via the cancel hole, the valve element is subjected to the suction pressure Ps from both sides of the upper and lower portions thereof. In addition, because the upper and lower portions of the valve element have the same sectional area, the valve element is not influenced by the discharge pressure Pd. Therefore, because pressure balance is always maintained in the upper and lower portions of the valve element, the valve opening and closing accuracy can be improved. In addition, because the cancel hole is provided in the valve element, the working of the cancel hole can be easily performed.
Furthermore, in a second aspect of the present invention there is provided a control valve for variable capacity compressors, which comprises a control valve body, a solenoid excitation part and a pressure-sensitive part. The solenoid excitation part is provided with a solenoid, a plunger moving vertically by the excitation of the solenoid and an attraction element on the lower side of the plunger. And the pressure-sensitive part is formed on the inner side of the attraction element. As a result, because the pressure-sensitive part is formed on the inner side of the attraction element, it is possible to ensure compact design of the control valve by reducing the diameter of the solenoid excitation part.
In the control valve for variable capacity compressors according to the present invention, the following preferred embodiments can be adopted.
The attraction element is in the form of a cylinder with a bottom opposed to the plunger. Alternatively, the attraction element comprises a cylindrical portion to be engaged with the inner side of the solenoid excitation part and a cover portion to be press-fitted to the upper end of this cylindrical portion.
The plunger is provided with a coolant vent in the interior thereof in the longitudinal axial direction. Alternatively, the plunger is provided with a slit on the side surface thereof in the longitudinal axial direction.
The solenoid excitation part is provided with a stem having an almost half-moon section for transmitting the motion of the above-described pressure-sensitive part to the plunger.